Field of the Invention
The present disclosure relates to a quant dot-polymer complex and a method for preparing the same, and more particularly, to a method for preparing a quantum dot-polymer complex that reduces the degradation under high-temperature high-humidity environments and preparing a film having a uniform thickness, a quantum dot-polymer complex prepared by using the same, and a light conversion film, a backlight unit, and a display device, which have the same.
Description of the Related Art
Liquid crystal displays (LCDs), plasma display panel devices (PDPs), electroluminescence displays (ELDs), field emission displays (FEDs), and the like are introduced as flat panel displays (FPDs) having advantages such as slimness, lightweight, low power consumption, and are replacing existing cathode ray tubes (CRTs).
Among these, LCDs have low power consumption, good portability, technology compactness, and high added-value. LCDs are also non-emissive type devices and thus do not form an image by itself. Also, since LCDs are light receiving displays that receive light incident from the outside to form an image, an additional light source is needed. Cathode fluorescent lamps (CCFLs) have been mainly used as light sources of LCDs in the past. However, CCFLs have difficulty in securing of brightness uniformity and are deteriorated in color purity if CCFLs are manufactured in large scale.
Thus, three-color light emitting diodes (LEDs) instead of the CCFLs are being used in recent years as light sources of LCDs. When three-color LEDs are used, a high color purity can be realized to implement high-quality images. However, since the three-color LEDs are very expensive, the manufacturing costs increase. As a result, relatively inexpensive blue LEDs are being used as light sources. For this, technologies for converting blue light into red light and green light by using a light conversion film including quantum dots (QDs) to realize white light are being researched.
When the light conversion films using QDs are manufactured, it is preferably to uniformly disperse the QDs into a matrix resin. That is, if the QDs are aggregated, the light emitted from a light source passes through at least two QDs and thus is reabsorbed thereby deteriorating the light emitting efficiency. However, currently produced QDs have surfaces that are capped by using hydrophobic ligands so as to improve dispersibility. Thus, the types of dispersible media is limited, and the types of resins used for manufacturing films is limited.
Light conversion films also include a barrier film attached on top and bottom surfaces of the light conversion film, and QDs located in an edge portion of the film become oxidized by oxygen or moisture permeated through a side surface not including a separate barrier unit. A matrix resin having a low penetration ratio with respect to oxygen or moisture may be used to prevent this phenomenon from occurring. However, QDs are not well dispersed into resins having low vapor-permeability and/or moisture-permeability.
To solve the above-described limitation, matrix resins having low vapor-permeability and/or moisture-permeability are heated at a high temperature and then mixed with QDs. However, since the QDs are easily degraded at a high temperature, the QDs are deteriorated in light emitting efficiency.
In addition, a method for preparing a light conversion film by dispersing quantum dots into a matrix resin including specific contents of a polyfunctional light-curable oligomer and monofunctional light-curable monomer, which have an acid value of about 0.1 mgKOH/g or less, and then curing the matrix resin is disclosed in Korean Patent Publication No. 10-2012-0035157. According to the above-described method, after the quantum dots are dissolved into the monofunctional light-curable monomer that is a nonpolar material, the monofunctional light-curable monomer is phase-separated from the polyfunctional light-curable oligomer having high viscosity to form an emulsion, and then the quantum dots are dispersed into the matrix resin in the form of the emulsion.
However, since each of the emulsions formed by the above-described method is temporarily maintained by the high viscosity of the polyfunctional light-curable oligomer, the emulsions may be fused with each other as a time elapses. As a result, each of the emulsions may increase in size, and thus, the emulsions may increase in size distribution. Thus, the emulsions each of which has a size similar to a costing thickness may exist. Accordingly, when coating is performed, the emulsions may be pushed by a coating bar to generate stripes in a costing direction or to increase in size toward an end of the film. As a result, it is difficult to prepare a light conversion film having uniform optical performance.